Bach 11 vs Bach 15
The Bach 11 has a wider cup diameter.
Mouthpiece A
Bach 11
• Baritone / Euphonium
Cup diameter24.70 mm / 0.9724 in
Cup depthDeep
Rim width—
Throat diameter5.85 mm / 0.2303 in
Backbore—
Finish—
Material—
Best suited for
Orchestral playing — large cup for full, dark tone
High-volume projection — open throat for power
vs
Mouthpiece B
Bach 15
• Baritone / Euphonium
Cup diameter24.40 mm / 0.9606 in
Cup depthDeep
Rim width—
Throat diameter5.85 mm / 0.2303 in
Backbore—
Finish—
Material—
Best suited for
Orchestral playing — large cup for full, dark tone
High-volume projection — open throat for power
Cup Diameter
The Bach 11 has a cup diameter of 24.70 mm / 0.9724 in compared to 24.40 mm / 0.9606 in on the Bach 15 — a difference of 0.30 mm / 0.0118 in. A wider cup generally produces a fuller, darker tone but requires more air support.
Cup Depth
Both mouthpieces share a deep cup depth, so the sound character from depth alone will be very similar.
Throat Diameter
Throat diameters are essentially identical at 5.85 mm / 0.2303 in, so resistance feel will be comparable.
Which is better?
Neither mouthpiece clearly dominates the other — the right choice depends on your embouchure, playing style, and the sound you're after. Try both if possible.